As is well known, nowadays a content distribution system with DRM (Digital Rights Management) becomes widespread. In the content distribution system with DRM, when a content distributor distributes contents including a video image and audio, the contents are distributed while encrypted in order to protect a content copyright, and the encrypted contents are received and decrypted with a legitimate information processing device to which the content distributor provides a content key, thereby preventing the illegal acquisition of the contents.
Specifically, the content key is stored in a protected area of a data storage module, such as an SD (Secure Digital) memory card. The data storage module encrypts and transmits the content key stored in the protected area upon a request from the information processing device that successfully performs mutual authentication.
Therefore, the information processing device generates a key in order to decrypt the encrypted content key acquired from the data storage module based on an authentication key included in application software running on an OS (Operation System) that is of own operating software of the information processing device, and the information processing device decrypts the encrypted contents using the content key decrypted by the key.
In the current content distribution system, key calculation processing is performed by application software of the information processing device. When an analyst seeking to illegally obtain the contents analyzes the key calculation processing, which is used to decrypt the encrypted content key, to obtain a value of the content key, the encrypted contents are decrypted by the content key, which allows the analyst to illegally obtain the contents.